Effect of temperature on dicyandiamide (DCD) longevity in pastoral soils under field conditions

•Dicyandiamide (DCD) degradation rate and mean soil temperature were linearly related.•At 8 and 16°C, estimated DCD half-lives were 39±6 and 25±3 days, respectively.•At a temperature, DCD degraded faster in soils in the field than in incubated samples. Data were analysed from five trials begun in autumn at a field site and a relationship between time for concentration of the nitrification inhibitor dicyandiamide (DCD) in soil to halve (t½, days) and the mean soil temperature (T, °C) was developed: t½=54–1.8T. For example, when T was 8 and 16°C, t½ was 39±6 and 25±3 days (±95% confidence limit), respectively. Previously, under laboratory conditions at equivalent temperatures, the corresponding values of t½ were 86±31 and 44±24days. Thus, the proportional responses of t½ to increasing T from 8 to 16°C were similar, but under field conditions t½ was about half that under laboratory conditions.